Fans are critical components of computers, providing cooling airflow to processors, microchips, and other components. When fans fail, internal temperatures rise, which at the least necessitates shutting down the computer and replacing the failed fan. At the worst, the fan failure goes unnoticed by support personnel, causing improper performance or even permanent damage to the computer. In either case, productivity decreases and cost increases. In addition, in some computing applications, such as computer servers, the computers must be run continuously, regardless of whether there is a fan failure.
A solution to this problem would be to install multiple fans to serve the computer. In this age of smaller and smaller computers, however, space is at a premium, and every fan added means larger computers, higher costs, and less space for other components. Fans installed in a parallel configuration take up significantly more room than a single fan alone, and the installation of the second fan may not be in a location that allows for optimal airflow over the computer components.
Fans installed in series suffer from different problems. If one fan is not functioning, the other fan would be operating less efficiently, trying to move air past the non-operational fan. If the non-operational fan is in a free-wheeling condition (i.e., spinning due to airflow over the blades), efficiency of the operational fan is still reduced. A locked-rotor condition in the non-operational fan poses an even greater obstacle to proper airflow. These conditions also may lead to reduced fan life for the operational fan. The solution to this problem would be to remove the non-operational fan from the path of the airflow, but this solution is not practical.
Another drawback associated with current tube axial fans is that the number of blades that can be formed on a given fan is limited by the construction of, and processes used to manufacture such fans. Typically, the greater the number of blades that can be formed on a tube axial fan of given size and geometry, the greater will be the flow rate of the fan at each pressure point (i.e., the pressure differential between the inlet and outlet of the fan during operation). Accordingly, in order to increase the flow rate of a tube axial fan of given size and geometry, it is desirable to maximize the number of blades on the fan. In certain applications, this may involve forming the blades in an overlapping manner (i.e., wherein the trailing edge of each blade angularly overlaps the leading edge of the adjacent blade). In many commercially available tube axial fans, the blades and rotor hub are formed of plastic and injection molded as a single part. Typically, the molding equipment requires that the adjacent edges of the blades be angularly spaced relative to each other (i.e., the trailing edge of each blade must be angularly spaced from the leading edge of the next blade). Otherwise, the manufacturing process would require overly complex and/or expensive molding equipment that would render the fan commercially impractical. Accordingly, it has been considered impractical to injection mold rotor hub and blade assemblies with overlapping blades. One manufacturer has provided a tube axial fan with overlapping blades by welding the blades to the rotor hub. However, this manufacturing process is believed to be relatively expensive and therefore undesirable in comparison to the processes used to injection mold conventional tube axial rotor hub and blade assemblies.
What is needed then, is a collapsible fan and fan system that provide redundant airflow to a computer or other electronic applications (e.g., communication, appliance and automotive applications) without taking up much more space than a single fan. Also, to reduce fan inefficiencies that occur when an operational fan attempts to move air past a non-operational fan, a collapsible fan and redundant fan system that minimize blockage by the non-operational fan would be desired. Collapsible fans already exist in applications other than computers or electronic applications wherein the fans fold during periods of non-operation, using a mechanical means (e.g., a spring), the dynamic pressure of the passive flow of fluid over the blades, or gravity. Some of these fans are forced open due to centrifugal motion when operating. None of these fans, however, address the problem of reduced fan efficiency in series mounted fans in the event of a fan failure. Similarly, none of the existing collapsible fans address the problem of continuously operating a computer or other electronic apparatus (e.g., communications equipment, appliances, and automotive equipment) in the event of a fan failure.
Accordingly, it is an object of the present invention to overcome one or more the above-described drawbacks and disadvantages of the prior art.